The programmer provides a specification of the program, in the form of
properties which functions should satisfy, and QuickCheck then tests that the
properties hold in a large number of randomly generated cases.

Specifications are expressed in Haskell, using combinators defined in the
QuickCheck library. QuickCheck provides combinators to define properties,
observe the distribution of test data, and define test data generators.

The official QuickCheck manual
explains how to write generators and properties;
it is out-of-date in some details but still full of useful advice.

Maintainer's Corner

Readme for QuickCheck-2.11.2

This is QuickCheck 2, a library for random testing of program properties.
Install it in the usual way:
$ cabal install
There is a Google group for user discussion and questions at
https://groups.google.com/forum/#!forum/haskell-quickcheck.